The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, a functional block diagram of an engine system 100 is presented. Air is drawn into an engine 102 through an intake manifold 104. A throttle valve 106 controls airflow into the engine 102. An electronic throttle controller (ETC) 108 controls the throttle valve 106 and, therefore, the airflow into the engine 102. The air mixes with fuel from one or more fuel injectors 110 to form an air/fuel mixture.
The air/fuel mixture is combusted within one or more cylinders of the engine 102, such as cylinder 112. Combustion of the air/fuel mixture may be initiated by, for example, injection of the fuel or spark provided by a spark plug 114. In spark ignition engine systems, a spark actuator module 116 controls the spark provided by the spark plug 114. Combustion of the air/fuel mixture produces torque and exhaust gas. More specifically, torque is generated via heat release and expansion during combustion of the air/fuel mixture within the cylinders. Torque is transferred by a crankshaft of the engine 102 through a driveline (not shown) to one or more wheels to propel a vehicle. The exhaust is expelled from the cylinders to an exhaust system 118.
An engine control module (ECM) 130 controls the torque output of the engine 102. The ECM 130 controls the torque output of the engine 102 based on driver inputs and/or other inputs. A driver input module 132 provides the driver inputs to the ECM 130. The other inputs include pressure signals (Cylp) from a cylinder pressure sensor 134 that measures pressure within the cylinder 112 (i.e., cylinder pressure).
The ECM 130 performs various computations based on the cylinder pressure. For example, the ECM 130 determines a pressure ratio for the cylinder 112 at various crankshaft angles. The pressure ratio is the ratio of the measured cylinder pressure at a crankshaft angle to a motored (ideal) cylinder pressure at that crankshaft angle. The motored cylinder pressure corresponds to an estimated cylinder pressure at the crankshaft angle if combustion did not occur within the cylinder 112. In other words, the motored cylinder pressure corresponds to an expected cylinder pressure at the crankshaft angle when the cylinder 112 is being motored. The motored cylinder pressure is computed based on an assumption that cylinder pressure changes as cylinder volume changes and that the cylinder pressure behaves polytropically based on the relationship below.P(Θ)=PO[VO/V(Θ)]γ,where P(Θ) is the cylinder pressure at a given crankshaft angle Θ, PO and VO are initial cylinder pressures and volumes, respectively, VΘ is the cylinder volume at the crankshaft angle Θ, and γ is a specific heat ratio.
The ECM 130 determines a heat release rate for the fuel injected, the quantity of fuel injected, and/or the cetane index (a measure of fuel ignitability). The ECM 130 may then adjust various parameters based on these measured and/or computed parameters, such as the timing of combustion. Combustion timing may be adjusted in a spark ignition engine via the spark timing and in a diesel engine via fuel injection timing. The ECM 130 may also adjust other parameters based on the parameters, such as the amount of fuel injected.